--- rxvt-unicode/configure.ac	2015/06/16 12:00:07	1.154
+++ rxvt-unicode/configure.ac	2021/05/13 19:40:27	1.156
@@ -3,9 +3,9 @@
 dnl#
 
 AC_INIT
-AC_PREREQ(2.50)
+AC_PREREQ(2.71)
 AC_CONFIG_SRCDIR([src/feature.h])
-AC_CONFIG_HEADER(config.h:config.h.in)
+AC_CONFIG_HEADERS(config.h:config.h.in)
 
 AC_CANONICAL_HOST
 
@@ -28,11 +28,13 @@
 AC_PROG_CXX
 AC_PROG_INSTALL
 
-AC_AIX
-AC_GNU_SOURCE
-AC_ISC_POSIX
+AC_USE_SYSTEM_EXTENSIONS
 AC_LANG(C++)
 
+if test "$ac_prog_cxx_stdcxx" != cxx11; then
+  AC_MSG_ERROR([the compiler does not support C++11])
+fi
+
 LINKER="$CXX"
 dnl check whether we can link with gcc -lsupc++
 if test x$GCC = xyes && test x$GXX = xyes; then